Generally, rotary-wing aircraft maneuver in part by changing the rotor blade angle of attack or pitch (e.g. the angle that each blade makes with the relative wind). Traditionally, changes in blade pitch have been accomplished via a swashplate connected to a pitch link/pitch horn assembly on each rotor blade. The orientation of the pitch link and pitch horn also allowed the blade pitch to change in response to blade lift and hence flapping differences that occur due to the dissymmetry of speed (e.g. between the advancing blade and the retreating blade) produced during forward flight. Rotary-wing aircraft designers refer to the angle between the location of the pitch link and a line perpendicular to the blade axis at the point the blade attaches to the hub as the delta-3 angle. The delta-3 angle is an important safety consideration in rotor hub design because it helps control the problems associated with the dissymmetry of lift that occurs in forward flight.
Active blade control is a concept that has received much attention lately. Active blade control allows the pitch of each individual rotor blade to be changed independent of the other rotor blades. Doing so allows the rotor blade pitch to be altered in ways that are not possible with swashplates, for example blade pulsing. However, helicopter manufacturers are reluctant to use active blade control because it eliminates the safety that is inherent in the mechanical pitch horn/pitch link system (e.g. the delta-3 angle). Therefore, a need exists for a swashplateless rotor hub assembly that controls pitch angle of the individual rotor blades while retaining the delta-3 angle.